1. Field of the Invention
The present invention relates to laser welding, heat treating and surface machining techniques, particularly to improvements in laser beam delivery systems.
2. Description of the Prior Art
It is well known that the welding of bellows or expandable bladders (shown in U.S. Pat. No. 4,102,438) by electron beam or laser welding techniques has a high cost and is a time consuming process implicating the repetitive welding of the inside-diameter edges and outside-diameter edges of each annular sheet forming the bellows.
It is also recognized that a major problem is the welding of relatively large diameter bellows (over 12 inches in diameter), particularly produced from relatively thin material (.+-.0.005"). The deformation produced by the thermal expansion from the repetitive welding generates stress at the welding seam which makes it very difficult, if not impossible, to produce fluid-tight bellows on a large scale, without suffering a high rate of rejects.
It is also well known that the tracking of a seam to be welded, using a focused circular beam centered on the seam, by electron scanning or other methods, reduces the linear welding speed in view of the reaction time delay involved, and that such tracking is limited to one seam at a time.
It is also well known that it is relatively easy to scan and control the focus of an electron beam from an electron beam welder at high speed (measured in KHZ) since the beam is deflected and focused electromagnetically when used principally for heat treating or surface machining. However, with laser equipment, the scanning and focusing of a laser beam is done mechanically through mirrors or lens, thus limiting the speed and precision thereof. Great strides were made in improving surface heat treating or machining with the use of electron beam high speed scanning. However, the high cost, complexity and the negative environmental impact of electron beam equipment have limited the use of this technique.
Another factor which has a serious cost impact in laser surface machining is the limited area covered by the laser focal beam at the working surface, thus requiring a large amount of beam scanning or work piece movements, to cover a working area larger than the focal beam diameter.